My DS is 22 months and has a strange way of getting himself to sleep. It's bizarre but I can only describe it as a humping like thing. He lays on his front and repeatedly brings his knees up under his body then back down again. It goes on for ages and he gets boiling. The only time he doesn't do it is when he falls asleep in the car. It's been going on for a few months now and I thought he'd grow out of it but he hasn't yet. Does anyone else's dc do this? Any advice generally on what we can do?